Waste heat boiler blowdown system

Abstract

The invention relates to the technical field of waste heat boiler blow-off, and discloses a waste heat boiler blow-off system which comprises a three-stage evaporation system, a high-pressure boiler barrel, a medium-pressure boiler barrel, a low-pressure boiler barrel and matched evaporators, the boiler barrels are fixed to a furnace top steel frame through a supporting structure, and a superheater system comprises a high-pressure first-stage superheater, a high-pressure second-stage superheater, a low-pressure superheater and a matched water spraying temperature reducing device. The reheater system comprises a first-stage reheater, a second-stage reheater and a water spraying desuperheater; the sewage discharging system comprises an accident water discharging pipeline, a regular sewage discharging pipeline and a continuous sewage discharging pipeline, all the sewage discharging pipelines are connected into the sewage discharging flash tank, and the boiler is composed of an inlet flue, a heat exchange chamber, an outlet flue and a chimney. Meanwhile, inferior hot steam in the system can be discharged in time, the steam quality and the heat energy conversion efficiency are ensured, flue gas waste heat within various temperature ranges can be recycled, and gradient utilization of the waste heat is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of waste heat boiler blowdown, in particular to a waste heat boiler blowdown system. BACKGROUND

[0002] The waste heat boiler is a kind of high-efficiency heat energy conversion equipment widely used in industrial and power generation fields, which produces steam by recycling and converting the waste heat in the work, so as to drive the steam turbine or other power system and realize the effective utilization of energy.

[0003] The traditional waste heat boiler design aims to maximize the energy conversion efficiency and effectively manage the thermal stress and pressure system in the boiler, however, the traditional waste heat boiler can usually only recover the flue gas waste heat in a certain temperature range, resulting in that the waste heat cannot be fully utilized, causing energy waste, in actual operation, with the increase of temperature and pressure, the boiler may produce sewage containing impurities and salt, if not timely excluded, these impurities and salt will gradually deposit and cause the performance of the equipment to decline, and even cause safety hazards, therefore, the waste heat boiler blowdown system is crucial to ensure the reliable operation of the waste heat boiler. SUMMARY

[0004] (I) Technical problems solved

[0005] In view of the deficiencies in the prior art, the present application provides a waste heat boiler blowdown system, which solves the problem that the traditional waste heat boiler can usually only recover the flue gas waste heat in a certain temperature range, resulting in that the waste heat cannot be fully utilized, causing energy waste, in actual operation, with the increase of temperature and pressure, the boiler may produce sewage containing impurities and salt, if not timely excluded, these impurities and salt will gradually deposit and cause the performance of the equipment to decline, and even cause safety hazards.

[0006] (II) Technical solutions

[0007] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0008] A waste heat boiler blowdown system, comprising the following components: a three-stage evaporation system: high-pressure, medium-pressure and low-pressure drums and matching evaporators, the drum is fixed to the furnace top steel frame through a support structure; a superheater system: including high-pressure primary and secondary superheaters, low-pressure superheaters and matching water spray cooling devices; a reheater system: including primary and secondary reheaters and water spray coolers; a blowdown system: including an emergency blowdown pipeline, a regular blowdown pipeline and a continuous blowdown pipeline, all blowdown pipelines are connected to a blowdown flash tank.

[0009] Further, the boiler is composed of an inlet flue, a heat exchange chamber, an outlet flue and a chimney, and is provided with a selective catalytic reduction denitration device; the boiler is of a three-pressure, once intermediate reheating, non-combustion supplementing, horizontal natural circulation structure; all the heating surfaces of the boiler are spiral-toothed angle finned tube, vertically arranged in the heat exchange chamber, and the upper and lower ends of the heating surface tube are respectively provided with an upper header and a lower header, and each header is provided with two lifting points to transmit the load of the tube bundle to the furnace top steel frame.

[0010] On the basis of the foregoing scheme, one drain pipe line is arranged for each of the high-pressure, medium-pressure and low-pressure drums, electric and manual stop valves are arranged, and the drains are discharged to a blowdown flash tank; a regular blowdown pipe line is led out from the bottom of the distribution header, a continuous blowdown pipe line is led out from the bottom of the drum, an electric valve is arranged in the main pipe, a manual valve is arranged in the branch, an electric blowdown valve is arranged at the bottom of the drum, and the blowdown is discharged to the flash tank.

[0011] As a further scheme of the present application, the high-pressure superheater adopts high-pressure feed water temperature reduction, the reheater adopts medium-pressure feed water temperature reduction, and both adopt multi-hole nozzle type temperature reducers; a high-pressure economizer is arranged at the feed water inlet side of the high-pressure drum, the high-pressure economizer is provided with a bypass system to control the outlet temperature, and an interface for a starting water supply pipe line is reserved.

[0012] Further, the heater is provided with a recirculation pipe line to prevent low-temperature corrosion, and in winter, the heater functions as a heating loop; the low-pressure drum supplies high-pressure and medium-pressure feed water pumps; medium-pressure feed water enters the medium-pressure drum through an economizer; and high-pressure feed water enters the high-pressure drum through a three-stage economizer.

[0013] On the basis of the foregoing scheme, all the heating surfaces of the boiler are arranged in the order of a two-stage reheater, a high-pressure two-stage superheater, a one-stage reheater, a high-pressure one-stage superheater, a high-pressure evaporator, a high-pressure three-stage economizer, a medium-pressure superheater, a medium-pressure evaporator, a low-pressure superheater, a high-pressure two-stage economizer, a medium-pressure economizer, a high-pressure one-stage economizer, a low-pressure evaporator and a condensate heater along the flow direction of flue gas.

[0014] As a further scheme of the present application, the high-pressure, medium-pressure and low-pressure drums form independent circulation loops through downcomers and evaporators; low-pressure steam is used for deaeration, and the rest is used for work; medium-pressure steam enters a medium-pressure cylinder after being reheated; and high-pressure steam enters a high-pressure cylinder after being superheated in two stages.

[0015] Further, the inlet flue is connected to the exhaust transition section of the gas turbine through an expansion joint.

[0016] A three-stage evaporation operation process of a waste heat boiler blowdown system is also provided, comprising the following steps:

[0017] S1: Condensate deoxygenation: After being heated by the condensate heater, the turbine condensate enters the deaerator through the regulating valve to remove oxygen. S2: Low-pressure boiler drum water supply: Deoxygenated water is directly introduced into the low-pressure boiler drum, and the saturated water in the boiler drum enters the low-pressure evaporator through the downcomer. S3: Low-pressure natural circulation: The steam-water mixture at the evaporator outlet returns to the low-pressure boiler drum, forming a natural circulation loop. S4: Low-pressure steam distribution: Part of the low-pressure saturated steam is supplied to the deaerator, and the remainder is sent to the turbine for power generation via the low-pressure superheater. S5: Heater corrosion prevention: The condensate heater recirculation pipeline is started to... S6: Heating operation circulation. During heating operation, some hot water is returned to the heater inlet by the recirculation pump after heat exchange in the heat network heat exchanger; S7: Medium-pressure system water supply. Low-pressure boiler drum feedwater is supplied to high and medium-pressure feedwater pumps. Medium-pressure feedwater enters the medium-pressure boiler drum through the economizer; S8: Medium-pressure steam generation. Saturated water in the medium-pressure boiler drum is circulated through the evaporator. Steam enters the medium-pressure cylinder of the steam turbine through the medium-pressure superheater; S9: High-pressure temperature control. High-pressure feedwater enters the high-pressure boiler drum through a multi-stage economizer. The economizer outlet temperature is controlled by the bypass system.

[0018] (III) Beneficial Effects

[0019] Compared with the prior art, the present invention provides a waste heat boiler blowdown system, which has the following beneficial effects:

[0020] 1. The waste heat boiler in this invention adopts a three-stage evaporation system and a single intermediate reheat structure, which can efficiently recover and utilize waste heat from flue gas at various temperature ranges, realizing the cascade utilization of waste heat. By optimizing the layout of the heating surface, the boiler extensively uses spiral toothed finned tubes with bends to enhance heat exchange efficiency. Combined with the vertical tube bundle design, the blowdown efficiency is improved, thereby ensuring uniform heat distribution on the heating surface and improving heat exchange performance. This design can not only significantly improve the energy conversion rate, but also effectively extend the service life of the boiler equipment.

[0021] 2. This invention features three independent sewage discharge pipelines, coupled with electric and manual dual valve sets, which can control the timing and amount of sewage discharge in a timely manner. This not only helps to keep the boiler interior clean and prevent scale buildup on the pipe walls and heating surfaces, but also allows for the timely removal of inferior hot steam from the system, ensuring steam quality and thermal energy conversion efficiency.

[0022] 3. In this invention, the high-pressure primary and secondary superheaters work together with the low-pressure superheater, the water spray desuperheating device precisely regulates the steam temperature, and the multi-hole nozzle desuperheater improves the atomization effect and avoids local overheating, thereby further improving the reliability of the equipment under various working conditions.

[0023] 4、The first and second reheaters in the application cooperate with water injection desuperheaters, effectively improve the enthalpy value of medium-pressure steam, reduce the risk of wet gas erosion of the last stage blade of the steam turbine, realize efficient energy conversion through the step-by-step process of deaeration of condensed water, low-pressure circulation, medium-pressure water supply and high-pressure temperature control, the recirculation pipeline of the heater is corrosion-resistant and takes into account the winter heating demand, and the three-stage economizer is arranged in series to maximize the recovery of flue gas waste heat. BRIEF DESCRIPTION OF DRAWINGS

[0024] Fig. 1 A module structure diagram of a waste heat boiler blowdown system is provided for the application.

[0025] Fig. 2 A three-stage evaporation operation flow diagram of a waste heat boiler blowdown system is provided for the application. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0027] Embodiment 1

[0028] Reference Figs. 1-2 A waste heat boiler blowdown system includes the following components:

[0029] A three-stage evaporation system: high-pressure, medium-pressure and low-pressure drums and matching evaporators, the drums are fixed to the furnace top steel frame through a support structure;

[0030] A superheater system: including high-pressure first and second superheaters, low-pressure superheaters and matching water injection desuperheating devices;

[0031] A reheater system: including first and second reheaters and water injection desuperheaters;

[0032] A blowdown system: including an emergency blowdown pipeline, a regular blowdown pipeline and a continuous blowdown pipeline, all blowdown pipelines are connected to a blowdown flash tank.

[0033] Especially, the boiler is composed of an inlet flue, a heat exchange chamber, an outlet flue and a chimney, and is provided with a selective catalytic reduction denitration device; the boiler is of a three-pressure, once intermediate reheating, non-combustion supplementing, horizontal natural circulation structure; the waste heat boiler adopts a three-stage evaporation system and a once intermediate reheating structure, can efficiently recover and utilize flue gas waste heat in various temperature ranges, realizes waste heat cascade utilization, all the heating surfaces of the boiler are spiral-toothed angle finned tubes, are vertically arranged in the heat exchange chamber, the upper and lower ends of the heating surface tubes are respectively provided with upper and lower headers, each header is provided with two lifting points to transmit the load of the tube bundle to the furnace top steel frame, through optimization of the layout of the heating surface, the boiler largely adopts spiral-toothed angle finned tubes, strengthens heat exchange efficiency, cooperates with the vertical tube bundle design, improves the blowdown efficiency, and further ensures uniform heat distribution of the heating surface, improves heat exchange performance, the high-pressure, medium-pressure and low-pressure drums are respectively provided with one blowdown pipeline, are provided with electric and manual stop valves, are discharged to a blowdown flash tank, a regular blowdown pipeline is led out from the bottom of the distribution header, a continuous blowdown pipeline is led out from the bottom of the drum, the main pipeline is provided with an electric valve, branch pipelines are provided with manual valves, an electric blowdown valve is arranged at the bottom of the drum, is centrally discharged to the flash tank, three independent blowdown pipelines are arranged, cooperate with the electric and manual double valve groups, can timely control the timing and quantity of blowdown, not only help to keep the inside of the boiler clean, avoid fouling of the tube wall and heating surface, but also can timely remove inferior quality hot steam in the system, ensure steam quality and heat energy conversion efficiency.

[0034] It should be noted that the high-pressure superheater adopts high-pressure feed water temperature reduction, the reheater adopts medium-pressure feed water temperature reduction, and both adopt multi-hole nozzle type temperature reducer; the high-pressure drum is arranged with high-pressure economizer at the feed water inlet side, the high-pressure economizer is provided with bypass system to control the outlet temperature, the starting water supply pipeline interface is reserved, the heater is provided with recirculation pipeline to prevent low-temperature corrosion, and the heater serves as heating circuit in winter; the low-pressure drum supplies high-pressure and medium-pressure feed water pumps; the medium-pressure feed water enters the medium-pressure drum through the economizer; the high-pressure feed water enters the high-pressure drum through the three-stage economizer; the high-pressure first-stage and second-stage superheaters and the low-pressure superheater work cooperatively; the water spray temperature reduction device precisely adjusts the steam temperature; the multi-hole nozzle type temperature reducer improves atomization effect and avoids local overheating; the operation reliability of the equipment under various working conditions is further improved; all the heating surfaces of the boiler are sequentially arranged along the flue gas flow direction as the second-stage reheater, the high-pressure second-stage superheater, the first-stage reheater, the high-pressure first-stage superheater, the high-pressure evaporator, the high-pressure three-stage economizer, the medium-pressure superheater, the medium-pressure evaporator, the low-pressure superheater, the high-pressure second-stage economizer, the medium-pressure economizer, the high-pressure first-stage economizer, the low-pressure evaporator and the condensate heater; the high-pressure, medium-pressure and low-pressure drums form independent circulation loops through the downcomer and the evaporator; the low-pressure steam is used for deaeration, and the rest is used for work; the medium-pressure steam enters the medium-pressure cylinder after passing through the reheater; the high-pressure steam enters the high-pressure cylinder after passing through the two-stage superheater; the inlet flue gas duct is connected with the exhaust transition section of the gas turbine through the expansion joint; the first-stage and second-stage reheaters in the application cooperate with the water spray temperature reduction device to effectively improve the enthalpy value of the medium-pressure steam, reduce the risk of wet gas erosion of the last-stage blade of the steam turbine, realize energy efficient conversion through the step-by-step process of condensate deaeration, low-pressure circulation, medium-pressure water supply and high-pressure temperature control, the heater recirculation pipeline prevents corrosion and meets the winter heating demand, and the three-stage economizers are arranged in series to maximize the recovery of flue gas waste heat.

[0035] The application further provides a three-stage evaporation operation process of a waste heat boiler blowdown system, which comprises the following steps:

[0036] S1: condensate deaeration; the steam turbine condensate is heated by the condensate heater, enters the deaeration head through the adjusting valve, and completes oxygen removal;

[0037] S2: low-pressure drum water supply; the deaerated water is directly introduced into the low-pressure drum, and the drum saturated water enters the low-pressure evaporator through the downcomer;

[0038] S3: low-pressure natural circulation; the evaporator outlet steam-water mixture returns to the low-pressure drum to form a natural circulation loop;

[0039] S4: low-pressure steam distribution; part of the low-pressure saturated steam is supplied to the deaerator, and the rest is sent to the steam turbine to do work through the low-pressure superheater;

[0040] S5: heater corrosion prevention; the condensate heater recirculation pipeline is started to improve the inlet water temperature and prevent low-temperature flue gas corrosion;

[0041] S6: Heating condition cycle, in heating condition, part of hot water is returned to the heater inlet by the recirculation pump after heat exchange in the heat network heat exchanger;

[0042] S7: Medium pressure system water supply, low pressure drum water supply to high and medium pressure feed water pumps, medium pressure feed water enters the medium pressure drum through the economizer;

[0043] S8: Medium pressure steam generation, medium pressure drum saturated water circulates through the evaporator, and steam enters the medium pressure cylinder of the steam turbine through the medium pressure superheater;

[0044] S9: High pressure temperature control, high pressure feed water enters the high pressure drum through the multi-stage economizer, and the economizer outlet temperature is controlled through the bypass system.

[0045] Example 2

[0046] Referring to Figs. 1-2 A waste heat boiler blowdown system, comprising the following components:

[0047] A three-stage evaporation system: high, medium and low pressure drums and supporting evaporators, the drums are fixed to the furnace top steel frame through a support structure, the boiler is composed of an inlet flue, a heat exchange chamber, an outlet flue and a chimney, and is provided with a selective catalytic reduction denitration device; the boiler is a three-pressure, once intermediate reheated, non-combustion supplemented, horizontal natural circulation structure; all the heating surfaces of the boiler are spiral toothed angle finned tube, vertically arranged in the heat exchange chamber, the upper and lower ends of the heating surface tube are respectively provided with an upper header and a lower header, each header has two lifting points to transmit the load of the tube bundle to the furnace top steel frame, the high pressure economizer is arranged at the feed water inlet side of the high pressure drum, the high pressure economizer is provided with a bypass system to control the outlet temperature, and a starting water supply pipeline interface is reserved; the waste heat boiler in the present application adopts a three-stage evaporation system and a once intermediate reheated structure, can efficiently recover and utilize flue gas waste heat in various temperature ranges, and realizes waste heat cascade utilization; through optimization of the layout of the heating surface, the boiler largely adopts spiral toothed angle finned tube, strengthens heat exchange efficiency, cooperates with vertical tube bundle design, improves blowdown efficiency, and further ensures uniform heat distribution of the heating surface, improves heat exchange performance, this design not only can greatly improve energy conversion rate, but also can effectively prolong the service life of the boiler equipment;

[0048] A superheater system: containing high pressure primary and secondary superheaters, low pressure superheaters and supporting water spray temperature reducing devices, the high pressure superheater adopts high pressure feed water temperature reduction;

[0049] A reheater system: containing primary and secondary reheaters and water spray temperature reducers, the reheater adopts medium pressure feed water temperature reduction, and adopts a multi-hole spray pipe type temperature reducer;

[0050] A blowdown system: including an accident blowdown pipeline, a regular blowdown pipeline and a continuous blowdown pipeline, all the blowdown pipelines are connected to a blowdown flash tank.

[0051] The high-pressure, medium-pressure and low-pressure boiler drums are respectively provided with a water drainage pipeline, and are provided with electric and manual stop valves, and are discharged to a blowdown flash tank; a regular blowdown pipeline is drawn from the bottom of a distribution header, a continuous blowdown pipeline is drawn from the bottom of the boiler drum, an electric valve is arranged in the main pipeline, a manual valve is arranged in the branch pipeline, an electric blowdown valve is arranged at the bottom of the boiler drum, and is centrally discharged to the flash tank; the three independent blowdown pipelines are arranged, and are matched with the electric and manual double valve groups, so that the timing and amount of blowdown can be controlled in time, which not only helps to keep the inside of the boiler clean and avoid the fouling of the pipe wall and the heating surface, but also can timely remove the poor quality hot steam in the system, ensure the steam quality and heat energy conversion efficiency, the heater is provided with a recirculation pipeline to prevent low-temperature corrosion, and in winter, the recirculation pipeline is used as a heating loop, the low-pressure boiler drum supplies the high-pressure and medium-pressure feed water pumps, the medium-pressure feed water enters the medium-pressure boiler drum through the economizer, the high-pressure feed water enters the high-pressure boiler drum through the three-stage economizer, the high-pressure primary and secondary superheaters and the low-pressure superheater work cooperatively, the water spray desuperheating device accurately adjusts the steam temperature, the multi-hole nozzle type desuperheater improves the atomization effect and avoids local overheating, and the operation reliability of the equipment under various working conditions is further improved, all the heating surfaces of the boiler are sequentially arranged along the flue gas flow direction as the secondary reheater, the high-pressure secondary superheater, the primary reheater, the high-pressure primary superheater, the high-pressure evaporator, the high-pressure three-stage economizer, the medium-pressure superheater, the medium-pressure evaporator, the low-pressure superheater, the high-pressure secondary economizer, the medium-pressure economizer, the high-pressure primary economizer, the low-pressure evaporator and the condensate heater, the high-pressure, medium-pressure and low-pressure boiler drums form independent circulation loops through the downcomer and the evaporator; the low-pressure steam part is used for deaeration, and the rest does work; the medium-pressure steam enters the medium-pressure cylinder after being reheated; the high-pressure steam enters the high-pressure cylinder after being superheated, the inlet flue is connected with the exhaust transition section of the gas turbine through the expansion joint, the primary and secondary reheaters in the application cooperate with the water spray desuperheater, the enthalpy value of the medium-pressure steam is effectively improved, the risk of wet gas erosion of the last stage blade of the steam turbine is reduced, the energy efficient conversion is realized through the step-by-step process of condensate deaeration, low-pressure circulation, medium-pressure water supply and high-pressure temperature control, the heater recirculation pipeline prevents corrosion and meets the winter heating demand, and the three-stage economizers are arranged in series to maximize the recovery of flue gas waste heat.

[0052] The application also provides a three-stage evaporation operation process of a waste heat boiler blowdown system, comprising the following steps: turbine condensate is heated by a condensate heater, enters a deaeration head through a regulating valve, and completes oxygen removal; deaerated water is directly introduced into a low-pressure drum, saturated water in the drum enters a low-pressure evaporator through a downcomer; a steam-water mixture at the outlet of the evaporator returns to the low-pressure drum, forming a natural circulation loop; part of the low-pressure saturated steam is supplied to a deaerator, and the rest is sent to a steam turbine through a low-pressure superheater; a condensate heater recirculation pipeline is started to increase the inlet water temperature and prevent low-temperature flue gas corrosion; in a heat supply condition, part of the hot water is heated by a heat network heat exchanger and then returned to the heater inlet by a recirculation pump; the low-pressure drum supplies feed water to high-pressure and medium-pressure feed water pumps; medium-pressure feed water enters a medium-pressure drum through an economizer; saturated water in the medium-pressure drum is circulated through an evaporator, steam enters a medium-pressure cylinder of the steam turbine through a medium-pressure superheater; high-pressure feed water enters a high-pressure drum through a multi-stage economizer, the economizer outlet temperature is controlled through a bypass system, and the efficient use and circulation of condensate and boiler feed water are realized to recycle turbine condensate, which is then heated and evaporated in the low-pressure and medium-pressure drums, the generated steam is supplied to the steam turbine after being heated by a superheater, and hot water is supplied for heating through a heat network heat exchanger, thereby effectively improving the thermal efficiency and economy of the system.

[0053] In the description in the present document, it should be noted that the relational terms such as first and second and the like are used only to differentiate one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus including a series of elements includes not only those elements, but also other elements not explicitly listed or inherent to such a process, method, article or apparatus.

Claims

1. A waste heat boiler blowdown system characterized by, The boiler comprises the following components: A three-stage evaporation system: high-pressure, medium-pressure and low-pressure drums and matched evaporators, the drums being fixed to the furnace top steel frame through a support structure; A superheater system: including high-pressure primary and secondary superheaters, low-pressure superheaters and matched water spray temperature reducing devices; A reheater system: including primary and secondary reheaters and water spray temperature reducing devices; A blowdown system: including an emergency blowdown pipeline, a regular blowdown pipeline and a continuous blowdown pipeline, all of which are connected to a blowdown flash tank.

2. A waste heat boiler blowdown system according to claim 1, characterized in that The boiler is composed of an inlet flue, a heat exchange chamber, an outlet flue and a chimney, and is provided with a selective catalytic reduction denitration device; The boiler is of a three-pressure, once-through intermediate reheating, non-combustion supplementing and horizontal natural circulation structure; All the heating surfaces of the boiler are spiral-toothed finned tube with an angle fin, which are vertically arranged in the heat exchange chamber, and the upper and lower ends of the heating surface tubes are respectively provided with an upper header and a lower header, and each header is provided with two lifting points to transmit the load of the tube bundle to the furnace top steel frame.

3. A waste heat boiler blowdown system according to claim 2, wherein, Each of the high-pressure, medium-pressure and low-pressure drums is provided with a blowdown pipeline, and is provided with an electric and a manual stop valve, and is connected to the blowdown flash tank, the regular blowdown pipeline is connected to the bottom of the distribution header, and the continuous blowdown pipeline is connected to the bottom of the drum, the main pipeline is provided with an electric valve, the branch pipelines are provided with manual valves, and the bottom of the drum is provided with an electric blowdown valve, and the blowdown pipelines are connected to the flash tank.

4. A waste heat boiler blowdown system according to claim 3, wherein, The high-pressure superheater adopts high-pressure feed water temperature reduction, the reheater adopts medium-pressure feed water temperature reduction, and both of them adopt multi-hole nozzle type temperature reducing devices; the high-pressure drum is provided with a high-pressure economizer on the feed water inlet side, the high-pressure economizer is provided with a bypass system to control the outlet temperature, and an interface for a starting water supply pipeline is reserved.

5. A waste heat boiler blowdown system according to claim 4, wherein, The heater is provided with a recirculation pipeline to prevent low-temperature corrosion, and is used as a heating loop in winter, the low-pressure drum supplies high-pressure and medium-pressure feed water pumps, the medium-pressure feed water enters the medium-pressure drum through an economizer, and the high-pressure feed water enters the high-pressure drum through a three-stage economizer.

6. A waste heat boiler blowdown system according to claim 5, wherein, All the heating surfaces of the boiler are arranged in the following order along the flue gas flow direction: secondary reheater, high-pressure secondary superheater, primary reheater, high-pressure primary superheater, high-pressure evaporator, high-pressure three-stage economizer, medium-pressure superheater, medium-pressure evaporator, low-pressure superheater, high-pressure secondary economizer, medium-pressure economizer, high-pressure primary economizer, low-pressure evaporator and condensate heater.

7. A waste heat boiler blowdown system in accordance with claim 1 wherein, The high-pressure, medium-pressure and low-pressure drums form independent circulation loops through the downcomer and the evaporator; the low-pressure steam is used for deaeration, and the rest is used for work; the medium-pressure steam enters the medium-pressure cylinder after being reheated; and the high-pressure steam enters the high-pressure cylinder after being superheated.

8. A waste heat boiler blowdown system according to claim 2, wherein, The inlet flue is connected to the exhaust transition section of the gas turbine through an expansion joint.

9. A three-stage evaporation process for a waste heat boiler blowdown system according to claim 1, wherein, The method comprises the following steps: S1: deaeration of condensate water, turbine condensate water is heated by a condensate heater, enters an oxygen removal head through a regulating valve, and completes oxygen removal; S2: water supply of the low-pressure drum, deaerated water is directly introduced into the low-pressure drum, and saturated water in the drum enters a low-pressure evaporator through a downcomer; S3: low-pressure natural circulation, a steam-water mixture at the outlet of the evaporator returns to the low-pressure drum to form a natural circulation loop; S4: low-pressure steam distribution, part of the low-pressure saturated steam is supplied to a deaerator, and the rest is sent to a steam turbine to do work through a low-pressure superheater; S5: corrosion prevention of the heater, a recirculation pipeline of the condensate heater is started to improve the inlet water temperature and prevent low-temperature flue gas corrosion; S6: Heating condition cycle, in heating condition, part of hot water is returned to the heater inlet by the recirculation pump after heat exchange in the heat network heat exchanger; S7: Medium pressure system water supply, low pressure drum feed water is supplied to the high and medium pressure feed water pump, and the medium pressure feed water enters the medium pressure drum through the economizer; S8: Medium pressure steam generation, the saturated water in the medium pressure drum enters the steam turbine medium pressure cylinder through the evaporator cycle and the steam passes through the medium pressure superheater; S9: High pressure temperature control, the high pressure feed water enters the high pressure drum through the multi-stage economizer, and the economizer outlet temperature is controlled through the bypass system.

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